1. Field of the Invention
The present invention relates to a premelting method for the raw materials for glass as well as an apparatus relevant thereto. To be more precise, it is intended to provide a method of premelting the raw materials for glass which is high in heat efficiency and demonstrates a superior controllability, together with a compact premelting apparatus, which is low in the cost of equipment, for use in practicing said method.
2. Description of the Prior Art
At the time of industrial manufacturing of flat glass, glass fiber, etc., a large-sized furnace, or a glass tank furnace, is usually employed, and all of such processes as the heating of raw materials for glass, melting and refining have hitherto been performed by means of a single glass tank furnace.
Illustrated in FIG. 1 is a longitudinal sectional view taken along the length of a conventional glass tank furnace 40. In this apparatus, the temperature within the furnace is so controlled as to attain the maximum at about the center of the glass tank furnace to cause an upwardly flowing stream to exist at region 41. The stream of glass circulates in the direction of the solid line arrows. The zone in front of the region 41, to wit, the left part in FIG. 1, constitutes the premelting zone 42 to perform the heating and melting of the raw materials for glass fed therein. The zone inbetween the region 41 and the throat 43 is the melting zone 44 for the purpose of further advancing the premelting of raw materials for glass so as to effect homogenization as well as defoaming. The part to the rear of the throat 43, to wit, the right part in FIG. 1, constitutes the refining zone 45 for the purpose of accelerating the refining.
In said premelting zone 42, replenishing raw materials for glass are supplied in proportion to the amount of glass drawn out of the furnace and are piled up on the premelted materials of glass, and the heating and premelting are performed by flames contacting with the surface layer portion of raw materials for glass together with heat conduction to the bottom portion thereof. As for the inner layer of said raw materials for glass, however, premelting is retarded as the heat conduction is impeded by the vitrified surface layer of materials for glass, and what is more, because of the high viscosity of the vitrified materials, the velocity of convection thereof in relation to the preceding premelted glass is very low. For such reasons, the thermal efficiency is very inferior, and a tremendous amount of fuel is required. Inasmuch as all the foregoing processes are to be performed by a glass tank furnace of poor heat transmission efficiency, there would arise a vicious circle that the furnace is required to be of a large size, and enlargement of the furnace leads to increase in radiation heat loss. Besides, when the furnace is of a large size, it would be attended with such demerits that it must employ high-grade refractory materials in abundance and it is apt to be damaged frequently, so that it is costly.